1. Field of the Invention
The present invention relates to timepieces and time correction methods.
2. Background Art
Conventional GPS (Global Positioning System) receivers locate their respective positions by receiving GPS signals from selected ones of many (for example, 28) GPS satellites. Each GPS signal includes a C/A (Coarse/Acquisition) code of a different numerical value, which in turn includes navigation data or messages. In the reception of the GPS signals, each receiver compares three or four desired selected C/A codes with those of GPS signals received simultaneously from the GPS satellites, thereby selecting the desired satellites. Then, the receiver locates its position based on the navigation data included in the GPS signals from the selected satellites and current time data that will be provided by a timekeeping unit provided in the receiver and that is hereinafter referred to as internal current-time data.
A technique is provided for correcting the internal current time of the GPS receiver using the time data included in the navigation data. A GPS receiver, for example disclosed in Published Unexamined Japanese Patent Application Hei 9-178870, receives GPS signals from a plurality of GPS satellites, locates the position thereof and corrects the internal current-time data.
This receiver requires to drive at least three reception channels simultaneously to receive corresponding GPS signals from the GPS satellites concerned, and hence consumes high power. In addition, there is a demand that the internal current-time data be corrected with high accuracy.
It is therefore an object of the present invention to reduce power consumed to correct the internal current-time using the GPS signals and to correct the internal current time with high accuracy. To this end, it is an object of the present invention to correct the internal current time by receiving GPS time data from the same GPS satellite from which the GPS time data was received in the previous time correction in the same range of time from which the GPS time data was received in the previous time correction.